German Patent Application No. DE 10 2005 022 761 A1 describes a charging device having an assigned control circuit, the switched-mode power supply transformer being used for performing a normal operation or a charging operation. In standby operation, in which the charging device is operated in a standby mode, an additional transformer, which is switchable using a separate power switch, is used for generating a supply voltage for the control unit. A disadvantage is that the charging device and its control circuit are complex with regard to circuitry and are thus expensive.